Green’s Dictionary of Slang

gage n.1

[SE gage, a measure or, alternatively, a pledge, and thus, in the drinking context, a toast]

1. [mid-15C–18C] (UK Und., also gauge) a mug holding a quart (2pt/1l) of beer; occas. a pint.

2. [17C–mid-19C] (also gagg) any mug or container.

3. [mid-17C–1940s] (also gagg) a pipe, a pipeful of tobacco.

4. [mid-19C] a small quantity; thus a gage of tobacco, a gage of gin.

5. [1930s–50s] (US Und.) cheap whisky.